Last year we had an earthquake – a very loud scraping and banging noise, accompanied by the walls of the house shaking for several seconds – confirmed by the Centre Sismologique Euro-Méditerranéen. So this morning, when I heard a similar enormous bang, I immediately assumed we had just experienced another tremblement de terre.
When I picked Lisa up from the school in Fontenay, where she gives English lessons once a week, she revealed that the bang, whatever it was, had swung the door open in their classroom. And Lynn back in Foussais had felt the earth move, so to speak 
, and heard her windows rattle. Along with the bang, there was also a gassy smell. Something big had definitely happened.
I checked on the CSEM website. There had been seismic activity at Rennes at 4:44am, but our event was much later than that. All very strange.
Anyway, when Joe returned from school, he had news for us. Turns out our “earthquake” was just a passing jet plane causing a sonic boom. And the gassy smell? Just a controlled leak from a nearby gas works. So, not really all that exciting in the end, unless gas leaks and sonic booms are your thing.
I’m still not totally convinced. A friend on Twitter heard the boom too, and she is 40 minutes away. That seems like one heck of a boom, but there appears to be no evidence to the contrary, so we’ll put this one down as a speeding aircraft…for now.
Still, it’s probably best that we didn’t have another earthquake. Although our house has stood strong for about 300 years, given our luck just recently, it would fall down around our ears if shaken too vigorously!
The sonic boom would be heard 40 miles away if the plane was heading in that direction. We were in Black Forrest a few years ago (23 years!) We heard loads of sonic booms and I was fascinated. The explanation for them is this:
When an airplane travels through the air, it produces sound waves. If the plane is traveling slower than the speed of sound (the speed of sound varies, but 700 mph is typical through air), then sound waves can propagate ahead of the plane. If the plane breaks the sound barrier and flies faster than the speed of sound, it produces a sonic boom when it flies past. The boom is the “wake” of the plane’s sound waves. All of the sound waves that would have normally propagated ahead of the plane are combined together so at first you hear nothing, and then you hear the boom they create.
It is just like being on the shore of a smooth lake when a boat speeds past. There is no disturbance in the water as the boat comes by, but eventually a large wave from the wake rolls onto shore. When a plane flies past at supersonic speeds the exact same thing happens, but instead of the large wake wave, you get a sonic boom. (Thanks you ‘How stuff Works’)